1. Field of the Invention
The present invention relates to a process for preventing the formation of harmful organic substances from organic building blocks. In particular, the invention relates to preventing the formation of dioxin and furan in the combustion of composite cobustible materials such as household, industrial, special or hazardous waste materials. The combustion occurs in a combustion chamber with the cooling and purification of the combustion gas occurring at the combustion-gas side. The invention also includes a steam generator for carrying out the process.
2. Description of the Prior Art
It is known that in the combustion of sulfur, SO.sub.2 and SO.sub.3 are formed in a particular ratio. In the incineration of waste, maximal SO.sub.3 levels emitted reach about 7 mg/m.sup.3.
It is also known (ATP 392,912 or 392,913) that in order to decrease the dioxin formation in the waste gas, SO.sub.2 can be fed to the combustion waste gas directly or indirectly through the additional combustion of sulfur-containing combustible materials (i.e., sulfur-containing waste materials). This suggestion, however, yields only a partial success even if relatively large amounts of sulfur are added since the dioxin content in the filter dust practically does not change. The filter dust includes metals such as copper, strontium, lead, iron, etc. with catalytic capabilities wherein the copper in combination with chlorine play a special role. See, for example, equations 1-4 below:
1) 2CuO+4HCl=2CuCl.sub.2 +2H.sub.2 O PA1 2) 2CuCl.sub.2 =2CuCl+Cl.sub.2 PA1 3) 2CuCl+1/2 O.sub.2 =Cu.sub.2 OCl.sub.2 PA1 4) Cu.sub.2 OCl.sub.2 +2HCl=2CuCl.sub.2 +H.sub.2 O
From these equations, it is evident that copper, through numerous conversions, can convert the combustion product HCl to chlorine and, in this way, exerts a catalytic effect for the (new) formation of PCDD/F. The chlorine generated (equation 2) combines with carbon compounds, aromatic compounds, and soot (i.e., non-burned residue) and forms chlorinated carbon compounds which include, among others, dioxins and furan.
The filter dust of waste material combustion installations contains approximately 0.1% copper and often more than 10% carbon. Thus, it must be taken into consideration that a major part of the metals being released in the combustion are eliminated with the slag or the combustion chamber ash in the combustion chamber free of dioxin.